Operation logic
67YN supports three operation modes selected with setting Operation mode: “General
EF”, “Alarming EF” and “Intermittent EF”.
Operation mode “General EF” is applicable in all kinds of ground faults in ungrounded
and compensated networks. It is intended to detect all kinds of ground faults regardless of
their type (transient, intermittent or restriking, permanent, high or low ohmic). The setting
Voltage pickup value defines the basic sensitivity of the 67YN function.
In “General EF” mode, the operate timer is started in the following conditions.
• Ground fault is detected by the General Fault Criterion (GFC)
• Fault direction equals Directional mode setting
• Estimated stabilized fundamental frequency residual current exceeds the set Min trip
current level
The PICKUP output is activated once Pickup delay time has elapsed. TRIP output is
activated once Trip delay time has elapsed and the above three conditions are valid. Reset
timer is started if any of the above three conditions is not valid. In case fault is transient and
self-extinguishes, PICKUP output stays activated until the elapse of reset timer (setting
Reset delay time). After TRIP output activation, PICKUP and TRIP outputs are reset
immediately, if any of the above three conditions is not valid. The pickup duration value
PICKUP_DUR, available in the Monitored data view, indicates the percentage ratio of the
pickup situation and the set operating time.
In case detection of temporary ground faults is not desired, the activation
of PICKUP output can be delayed with setting Pickup delay time. The
same setting can be also used to avoid restarting of the function during
long lasting post-fault oscillations, if time constant of post-fault
oscillations is very long (network losses and damping is low).
To keep the operate timer activated between current spikes during
intermittent or restriking ground fault, the Reset delay time should be set
to a value exceeding the maximum expected time interval between fault
spikes (obtained at full resonance condition). Recommended value is at
least 300 ms.
Section 4 1MAC059074-MB A
Protection functions
450 615 series ANSI
Technical Manual
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